Polymer electrolyte fuel cells (PEFCs) have great potential as an environmentally friendly energy source. Fuel cells have been used in the space program since the 1960's, but recently with the focus on “green” resources, fuel cells have come to the forefront of commercialization. Specifically, fuel cells are being explored for use in automobiles, electronics, and stationary power applications.
A polymer electrolyte fuel cell typically includes membrane electrode assembly (“MEA”) positioned between a pair of gas diffusion layers. The MEA typically includes a cathode and an anode with an exchange membrane positioned between the anode and cathode. A catalyst is used in proximity to the cathode and the anode.
For the last 30 years, the industry standard for the proton exchange membrane (PEM) as well as the electrodes for the fuel cell has been Nafion® (polyperfluoro sulfonic acid) by DuPont.
Nafion® materials display sufficient proton conductivity (˜0.1 S/cm), good chemical resistance, and mechanical strength. Some of the disadvantages of Nafion® materials include high cost, reduced conductivity at high temperatures (>80° C.), and high methanol permeability in direct methanol fuel cells.
Because of the renewed interest in fuel cells and the challenge of high temperature and direct methanol operation, new materials have been explored as potential replacements for Nafion®. Previous work has focused on sulfonated polystyrene, styrene-butadiene block copolymers, or poly(arylene ether)s such as PEEK. Typically, these polymers were all made by a post-sulfonation polymer modification reaction where the sulfonic acid groups are attached to the already formed polymer backbone.